How to get the correct Unix Timestamp from any Date in JavaScript

A generic solution to get the Unix timestamp of any JavaScript Date object.

// Copy & Paste this
Date.prototype.getUnixTime = function() { return this.getTime()/1000|0 };
if(!Date.now) Date.now = function() { return new Date(); }
Date.time = function() { return Date.now().getUnixTime(); }

// Get the current time as Unix time
var currentUnixTime = Date.time();
currentUnixTime = Date.now().getUnixTime(); // same as above

// Parse a date and get it as Unix time
var parsedUnixTime = new Date('Mon, 25 Dec 1995 13:30:00 GMT').getUnixTime();
// parsedUnixTime==819898200

Motivation

Unix time (AKA epoch time) is used widely in Unix-like and many other operating systems and file formats. Unfortunately, there's a small discrepancy between the C-style time() call and JavaScript's Date.getTime():

A Unix timestamp is defined as the number of seconds that have elapsed since 00:00:00 Coordinated Universal Time (UTC), Thursday, 1 January 1970.

JavaScript's Date.getTime() returns the numeric value of the specified date as the number of milliseconds since January 1, 1970, 00:00:00 UTC (negative for prior times).

Solution

Copy & paste the following code at the beginning of your JavaScript:

Date.prototype.getUnixTime = function() { return this.getTime()/1000|0 };
if(!Date.now) Date.now = function() { return new Date(); }
Date.time = function() { return Date.now().getUnixTime(); }

*** Done! ***

Usage

The three lines above add:

• Date.getUnixTime() returns the Unix epoch time.
• Date.now() polyfill for older browsers.
• Date.time() is a a C-style helper function that returns the current Unix time.

Get the current time as a Unix timestamp

var currentUnixTime = Date.time();

which is short for

var currentUnixTime = Date.now().getUnixTime();

Get the current time as JavaScript Date Object

var currentTime = Date.now();

Get the Unix time of any JavaSript Date object

var someDate = new Date('Mon, 25 Dec 1995 13:30:00 GMT');
var theUnixTime = someDate.getUnixTime();

Related work

• MomentJS is an excellent library to parse, manipulate, and format Date and Time values in JavaScript
• Questions on StackOverflow: How do you get a timestamp in JavaScript? and How to get current epoch/unix time in JS?

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